Why are some of the paving blocks pitted? - New driveway

[Bookie]

Hi all,
Thanks in advance for reading!

I've had my drive block paved in the last few weeks and am concerned at the number of pitted blocks. I would say the number constitutes around 5-10% of them. I've uploaded an example one in the link further below.

I cannot recall seeing any pitted blocks when they were first laid, and am puzzled as to what is causing them. I do park my car on the drive, though there is no sign of the drive sinking - nor is there an obvious sign that they are crumbling any further. Would appreciate any views/opinions as to what I should do.

Thanks!
Bookie


My Webpage

[Tony McC]

There's nothing wrong with those blocks. The tiny 'pits', as you call them, are perfectly normal for a block of that type.

When the damp concrete is placed into the mould (see this page), there is almost always a small amount of air trapped beneath the concrete. The press comes down and most of this air will be expelled but, in most manufacturing processes, a number of small air pocket will remain.

Here's an image of typical blocks that are deemed to be perfectly acceptable....



....I'd say the 'pits' in these blocks are more significant than those in your blocks, yet they are functioning perfectly well on a major commercial development.

There are tweaks that can be undertaken by the manufacturer to eliminate virtually all of these air pockets (such as adjusting the mix used for the face of the blocks) but in most cases, the cost of these tweaks is not justified by the extremely minor benefits gained.

In some manufacturing processes, a pocket of air is trapped, a thin 'film' of cementitious material may cover the void and give the impression of a pit-free surface, but as soon as the blocks are trafficked, this film breaks up and the miniscule pits are revealed.

These pits are a purely cosmetic issue. I have seen blocks where significant pitting has occurred, and that would be an issue worth pursuing with the manufacturer but, judging from the photie you posted, these barely even qualify as 'pits' at all. They are tiny pin-prick voids and in no way compromise the serviceability or the appearance of the pavement.

It's not unusual for owners of new paving to pore over every square millimetre of it and notice every minute difference and variation, every infinitesimal defect or mote of imperfection. We live in a universe of entropy. There is no such thing as perfection. You will find a fault, a deficiency, an error, a blemish, in almost every pavement ever laid. That's the nature of the world in which we live.

Trust me: in 3 months, you won't even notice these 'pits'!

[Bookie]

Hi Tony, thanks for taking the time to reply. I'm not sure if my photo clarifies it, but the chip missing measures 3cm * 2cm as its widest points. There are about 20 such blocks in this state. These are really like small chunks missing. Your photo shows what seem to be much smaller holes/bits missing. I'd have no issue with the blocks you display, but in my case, mine look a lot more unsightly.

Looking at a neighbour's block paving, they don't seem to have such issues on their blocks. The guy who did the block paving came over and said he'd replace the 20 or so blocks in this state, saying that the wacker plate may well have dislodged what was already loose.

I'm not sure whether to accept the offer and this compromise the integrity of the drive. Would appreciate your view.

Thanks again!

[mickg]

yes the blocks what are badly damaged need replacing

It could have been caused by the vibrating plate with the final compaction or damaged in transit

[Bookie]

Thanks for your confirmation, Mick!

[Tony McC]

I looked again at your photo but still can't see 2-3mm holes.

I *can* see bloody annoying pop-up ads and suspect survey requests, but that's the price we pay for so-called 'free' services.

If the pits are that size, then yes: they are not acceptable, but all I can see in the one photie which comes up are tiny pin pricks, <1mm in diameter

[Bookie]

Hi Tony,
Thanks for your response. Let me stress, the holes are 2cm-3cm (not mm). I counted 50 blocks with around 1cm holes, and of those, 30 have 2-3cm holes. The builder has agreed to replace the worst. I suppose that really it might be easier to replace the whole lot as the 30 blocks are fairly well scattered.

Thanks

[Tony McC]

Sorry - Meant to type cm, but my fingers automatically go to mm when discussing mesurements!

[mickg]

These are the marks/damaged blocks what I am seeing on the photo, what are you seeing Tony ?

[Bookie]

That's exactly it, Mick. For some reason, I didn't see them when laid, though there are 50 odd blocks like that now. None of them seem to be crumbly, so don't give the impression they will worsen. I'm not sure if the sealing that was done within 48 hours has made the holes more visible. Anyway, the builder has agreed to replace the worst 30 of them, though about 20 will still be present with smaller holes. I think replacing any higher a number than that would probably make it seem like the lot should be replaced.

Thanks

[Tony McC]

I thought that was a stain! My eyes aren't what they were.

It's called 'plucking' and it tends to happen with older moulds and/or moulds that haven't been adequately coated with a release agent. In essence, some of the concrete mix sticks to the mould and gets 'plucked' from the body of the block when it's de-moulded.

Should have been pulled by the installer.

[mickg]

I've booked you an appointment for next Friday 10am

this will sort you out Tony

[Bookie]

Thanks, guys - fantastic forum. I'll pass the word whenever the opportunity arises!

[Tony McC]

I've booked you an appointment for next Friday 10am

I use the one in Leigh - It's easier to understand the accent! ;~)

Joo-leh from Atherton sorts out me new goggles when I need them.